Attributes in .NET

Introduction to Attributes

Attributes in .NET provide a way to add metadata, declarative information, and behavior to program elements like classes, methods, properties, and parameters.

Using Built-in Attributes

.NET provides several built-in attributes like [Obsolete], [Serializable], and [Conditional] which can be applied to indicate deprecation, serialization support, and conditional compilation respectively.

using System;

[Obsolete("This method is deprecated. Use NewMethod instead.")]
public class MyClass {
    [Conditional("DEBUG")]
    public void DebugMethod() {
        Console.WriteLine("Debugging...");
    }
    
    [Serializable]
    public class SerializableClass {
        public string Name { get; set; }
    }
}
    

Creating Custom Attributes

You can create your own custom attributes by defining classes that inherit from System.Attribute. Custom attributes can be used to annotate code with domain-specific metadata.

using System;

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class MyCustomAttribute : Attribute {
    public string Description { get; set; }

    public MyCustomAttribute(string description) {
        Description = description;
    }
}

[MyCustom("This class represents a data entity.")]
public class DataEntity {
    [MyCustom("This method performs data validation.")]
    public void ValidateData() {
        // Validation logic
    }
}
    

Accessing Attributes at Runtime

Reflection in .NET allows you to inspect and retrieve attributes applied to types and members at runtime, enabling dynamic behavior based on metadata.

using System;
using System.Reflection;

public class Program {
    public static void Main() {
        Type type = typeof(DataEntity);
        var classAttributes = type.GetCustomAttributes(typeof(MyCustomAttribute), false);
        
        foreach (MyCustomAttribute attribute in classAttributes) {
            Console.WriteLine($"Class Attribute Description: {attribute.Description}");
        }
        
        MethodInfo method = type.GetMethod("ValidateData");
        var methodAttributes = method.GetCustomAttributes(typeof(MyCustomAttribute), false);
        
        foreach (MyCustomAttribute attribute in methodAttributes) {
            Console.WriteLine($"Method Attribute Description: {attribute.Description}");
        }
    }
}
    

Conclusion

Attributes in .NET offer a powerful mechanism to annotate code with metadata and behavior, allowing for declarative programming and dynamic behavior based on runtime inspection.